Inhibitory effects of scorpion venom on the uptake of amino acids by synaptosomes and synaptosomal membrane vesicles.

Scorpion (Tityus serrulatus) venom strongly inhibited the Na+-dependent uptake of (( 14C ))proline by rat brain synaptosomal preparations. In addition, the efflux of proline was enhanced markedly by scorpion venom. The inhibitory effects of the venom were also demonstrated in synaptosomal vesicle preparations where proline uptake was energized by an artificially imposed Na+ gradient. In both preparations, the effect of scorpion venom was additive with the inhibitory effect of veratridine on Na+-dependent amino acid uptake. The inhibitory effects of both compounds were abolished by tetrodotoxin. The Na+-dependent uptakes of amino acids (e.g. proline, glutamic acid, and gamma-aminobutyric acid) were much more sensitive to inhibition by the toxin than the Na+-independent uptakes (e.g. leucine and phenylalanine). The results of the present study indicate that the scorpion venom may exert its inhibitory effect on Na+-dependent transport by decreasing the transmembrane Na+ gradient. Efflux of accumulated proline, which is presumably controlled by maintenance of this Na+ gradient, was stimulated 3- to 4-fold by the scorpion venom.